The SRD on Ex-Paladins says
Like a member of any other class, a paladin may be a multiclass character, but multiclass paladins face a special restriction. A paladin who gains a level in any class other than paladin may never again raise her paladin level, though she retains all her paladin abilities.
My understanding is that, for example, a character that's a level 7 paladin who advances to level 8 and takes a level of rogue (so that he's a paladin 7/rogue 1) retains his paladin abilities but won't ever be able to become a level 8 paladin.
But how does that affect prestige classes? My understanding is that taking levels of a prestige class is different from multiclassing: taking a level in a prestige class is like a specializing in what the character already does, but taking a level in a base class—actual multiclassing—is like embracing a completely different and new path, position, or profession.
So some prestige classes are set up for paladins, like anointed knight (Book of Exalted Deeds 49-51), but does anything prevent a paladin from taking levels in a prestige class not directly related to paladins for which the character qualifies? I mean, can a paladin take levels in, for example, tempest (Complete Adventurer 81-2)?
So far as I can tell, nothing prevents a character with levels in paladin from taking a prestige class the character qualifies for, but one of my players says that if the prestige class doesn't specifically say a paladin can take levels in the prestige class, a paladin can't take levels in the prestige class.
So my question is this: Does anything in the rules stop a paladin from taking any prestige class for which he meets the requirements?